Mixing box for air conditioning system



July 2, 1968 R. E. PIERCE 3,390,623

MIXING BOX FOR AIR CONDITIONING SYSTEM Filed July 8, 1966 INVENTOR. Poe! 6. /epca 7Z-w/vEs 1 [is 7.40

Jay/v 6'. M P46 United States Patent 3,390,623 MIXING BOX FOR AIR CONDITIONING SYSTEM Robert E. Pierce, Farmington, Mich., assignor to American Radiator & Standard Sanitary Corporation, New York, N.Y., a corporation of Delaware Filed July 8, 1966, Ser. No. 563,784 6 Claims. (CI. 98-38) ABSTRACT OF THE DISCLOSURE This invention is directed to an air conditioner mixing box for central station units, and particular to air slicing mechanisms within the box for causing the two incoming air streams to properly mix together, thus avoiding stratification. The slicing mechanisms preferably take the form of parallel air separator strips extending within the box obliquely across the box corner areas in line with the respective air inlets, the strips for the different inlets being staggered to form air slices which merge together in sandwich fashion.

This invention relates to air conditioners, particularly central station air conditioners located in industrial and public buildings for supplying conditioned air to ducts which distribute the air throughout the buildings. Such central station air conditioners usually include a mixing box for mixing fresh air with return air, a filter box receiving the mixed air stream, a heating coil and/or cooling coil for treating the filtered air, and a centrifugal fan for drawing the treated air through the conditioner and discharging same into the distribution ductwork.

The present invention is particularly concerned with a novel construction of the mixing box used in central station air conditioners. The invention is generally directed to a new way of attaining the features of improvement mentioned in US. Patent 3,212,424. One object of the present invention is to provide a mixing box wherein two entering air streams are so merged or mixed together as to avoid stratification in hot and cold layers.

Another object is to provide a mixing box which delivers a fairly uniform temperature air stream across its outlet opening so that none of the air is so cold as to cause freeze-up of the heat exchange coil located downstream therefrom.

A further object is to provide a mixing box which accomplishes satisfactory mixing without necessitating the use of a large number of damper vanes or connecting linkages.

A still further object of the invention is to provide a new mixing box having improved performance, but without extensive alteration or redesign of existing mixing box construction.

An additional object is to provide an improved performance mixing box which has its inlets arranged in any of several selected locations, whereby to adapt the box to different field systems.

In the drawings:

FIG. 1 is a sectional view of a mixing box incorporating the invention, taken on line 11 in FIG. 2.

FIG. 2 is a sectional view taken essentially along line 22 in FIG. 1.

FIG. 3 is a fragmentary sectional view taken on line 3-3 in FIG. 2.

FIG. 4 is a blown up view of a fragmentary portion of the structure shown in FIG. 1.

FIG. 5 is a side elevational view of a second mixing box incorporating the invention.

General environment Referring more particularly to the drawings, there is 3,390,623 Patented July 2, 1968 shown a central station air conditioner mixing box 10 having two parallel side walls 12 and 14 interconnected by four elongated transverse walls 16, 18, 20 and 22. Located in wall 16 is a first fresh air inlet 24 comprising a hollow rectangular duct section 26 formed by elongated walls 28 and short end walls 30. As shown in FIG. 2, the duct may be equipped with a partition 32 to support the intermediate portions of damper shafts 34. The volume control damper vanes 36 are of course secured to shafts 34 and extend substantially the entire distance between walls 30 and 32. The vanes are of sufficient width as to completely close the air inlet 24 upon counter-clockwise rotation of shafts 34. Shaft rotation may be effected by a conventional lever 38 (FIG. 2) connected to a connecting rod 40. FIG. 5 shows the general nature of the shaft 34-connecting rod 40 relationship. Suitable linkages (not shown) may be located adjacent wall 32 to operatively inter-connect shafts 34 for conjoint movement.

A second return air inlet 42 may be formed in wall 18 by elongated walls 44 and short interconnecting walls 46. Inlet 42 is similar to inlet 24 in size and construction, and is provided with movable volume control damper vanes 36 carried by damper shafts 34. One of the shafts may be equipped with a lever which connects with the lower end of connecting rod 40, thus enabling all four of the damper vanes to be actuated by a single damper motor.

The general arrangement is such that air flow rates through the respective inlets are inversely proportional to one another, i.e., as the volume through inlet 24 increases the volume through inlet 42 decreases, and vice versa. The proportion of fresh air to recirculated air is thus varied in accordance with demands of the system. It will be understood that the air is discharged from box 10 through the single outlet 47. In the usual installation this outlet communicates with a filter section located upstream from one or more heat exchange coils. A centrifugal blower moves the air from the mixing box through the filter and coil sections to the distribution ductwork.

The invention The mixing box structure described above is conventional. The present invention concerns novel means for separating the individual air streams coming through inlets 24 and 42 into a multiplicity of air slices, and causing said slices to pass between one another in sandwich relation so as to mix together instead of recoiling from one another by direct impingement.

The air separating mechanism shown in FIGS. 1 and 2 comprises a first lower frame structure 48 and a second upper frame structure 50. Frame structure 48 comprises a first mounting bar 52, a second mounting bar 54, and five channel shaped air separator strips 56. The frame structure may be formed as a subassembly with the end portions of channels 56 secured to bars 52 and 54. The subassembly may then be installed in the mixing box as a unit.

Upper frame structure 50 comprises an upper transverse mounting bar 58, a lower transverse mounting bar 60 and six interconnecting air separator strips 62 of channel cross section. The upper frame structure may be formed as a subassembly and subsequently installed in its illustrated position.

During service the air flowing through inlet 42 strikes strips 56 and separates into vertical slices. Similarly the air flowing through inlet 24 strikes strips 62 and separates into individual vertical slices. It will be seen from FIG. 2 that air separator strips 56 occupy vertical planes which are staggered or offset from the planes occupied by separator strips 62. Thus the air flowing horizontally from inlet 42 against strips 56 will be separated into slices which are offset with respect to the air slices flowing downwardly between strips 62. The horizontally moving and vertically moving slices will tend to pass alongside one another and thus penetrate deeply into box it) without directly recoiling from one another by direct impingement. The return air will thus more intimately mix with the fresh air so that the air mixture discharged through outlet opening 47 will have a greater uniformity in temperature than would otherwise be possible.

Mixing is somewhat improved by the fact that the air slices flowing downwardly from strips 62 strike the rear faces of strips 56 and are deflected toward outlet 47; this tends to prevent the fresh air flowing through inlet 24 from blowing excessively down into the bottom portion of outlet 47. The air flowing through inlet 42 is given an upward deflection by damper vanes 36 when said vanes are in their illustrated partially open position; this may have a tendency toward improved mixing.

It will be seen that strips 56 and 62 are relatively wide; they are however only about half as wide as the spaces between the strips. Thus, the air slices are appreciably wider than the spaces between slices so there is some impingement or direct recoiling between the oncoming slices. This produces enough reaction between slices to promote mixing. Wider strips having the same width as the spaces between strips were tried. However the wider strips were apparently so effective that the oncoming slices actually appeared to blow by one another without effectively mixing. Thus, with seventy degree air flowing downwardly through inlet 24 and one hundred twenty degree air flowing through inlet 42 the outlet air temperature was found to be materially higher across the upper portion of the outlet. By using the illustrated strips of lesser width than the intervening spaces it was possible to appreciably improve the outlet temperature uniformity from top to bottom. The narrower strips are believed to make the spaces between air slices small enough so that the oncoming air slices must mix rather than blow by one another. The number of separator strips 56, 62 and intervening spaces in the illustrated box could be increased but such an expedient would so narrow the slices in each stream that they would merge soon after passing the strips and would not cross over for proper mixing. The width of the strips also depends on box height. A relatively small number of wide separator strips is believed to be the best compromise for most mixing boxes.

It will be understood that mixing boxes of different transverse width will require different numbers of air separator strips 56 and 62. With a box having a transverse dimension of about seventy inches and a vertical dimension of about thirty-five inches satisfactory results have been achieved with air velocities up to 900 feet per minute using four separator strips 56, each having transverse widths of four and a half inches and a spacing between strips of about seven and a half inches. In a larger mixing box having a transverse dimension of about one hundred twelve inches and a vertical dimension of about thirty-nine inches satisfactory results have been achieved using seven separator strips 56, each about four and a half inches wide, with a spacing between strips of about eight inches. The number of strips 62 will of course vary with the number of strips 56 used in any given installation. In some cases it may be necessary to provide narrow filler strips 62a at the ends of the box as shown in FIG. 2. These were added to preclude the end edge portions of the inlet 24 air stream from remaining in a non-mixed condition; note in this connection that the end air slices in the inlet 2-4 stream are only about half a wide as the other slices so that they apparently can be assimilated with the adjacent slices from inlet 52 even though there is only one mixing interface. The improvement with strips 62a may be considered somewhat marginal, and cost considerations might in any given installation dictate their elimination.

As shown in FIG. 1, the mixing box is provided with a fresh air inlet 24 in its upper transverse wall and a return air inlet 42 in one of its vertical transverse walls. Other inlet locations may be employed. For example, as shown in FIG. 5, either one of the inlets can be located in the upper transverse wall 16 or lower transverse Wall 20. With one of the inlets located in lower wall 20 the other inlet could be located in the upper portion of vertical wall 18 in the area generally designated by numeral 19. The FIG. 5 arrangement may have some slight advantages in performance because each set of separator strips act as batlies to deflect the oncomin air slices toward outlet 4-7, thus minimizing any tendency of the air streams to blow through to the opposite end of the outlet.

Whatever the location of the individual air inlets, each inlet is preferably located adjacent one corner of the box remote for air outlet 47; the respective inlets are however located remote from one another so that each one directs air into its own slicing mechanism. With the air inlets thus located, the air separator structures 48 and 50 can be located in the same positions in the box irrespective of the exact location of each inlet. For example, it will be noted that separator structures 48 and 50 occupy the same positions in the box of FIG. 5 as they do in the FIG. 1 box. This contributes to standardization of parts and easier installization of the separator structures on a semi-mass production basis.

As before noted, the mixing box is a conventional structure used prior to this invention. The structure is a rather simple mechanism employing but four damper vanes and a rather simple linkage control mechanism. The newly used separator structures 48 and 50 have been specifically designed to be accommodated in the conventional box without increasing the number of damper vanes, linkages, and control components. This is advantageous for example over the arrangement shown in aforementioned US. Patent 3,212,424. Thus, it will be seen that the patented arrangement employs a large number of short dampers arranged on axes parallel to the sidewalls of the mixing box. The large number of dampers requires a corresponding large number of interconnecting linkages and control rods, thus materially increasing costs. It will also be noted that in the patented arrangement the dampers necessarily move in opposite directions to maintain the parallel flow pattern of the individual streams. This opposite directional movement of the dampers necessitates additional linkage over and above the linkages employed in the damper arrangement of the present invention; in effect the patented arrangement requires two sets of parallel links movable in opposite directions but connected together for conjoint movement by an operator linkage. The resent invention economizes by way of reduction in the number of volume control vanes and control linkages.

It is believed that a mixing box constructed as shown herein can be manufactured at relatively small additional cost over conventional mixing boxes not having the im proved mixing action. Some variation in construction of the air separating components 48 and 50 is of course possible without departing from the concept of the invention as recited in the appended claims.

I claim:

1. An air conditioning system comprising a mixing box having two parallel side walls, and first, second, third and fourth transverse walls extending therebetween; means defining a first air inlet in the first transverse wall; means defining a second air inlet in the second transverse wall; means defining an air outlet in the third transverse wall; first volume control means for the air flowing through the first inlet; second volume control means for the air flowing through the second inlet; first mechanism immediately downstream from the first inlet separating the entering air stream into a multiplicity of air slices having planes parallel to the aforementioned side walls; second mechanism immediately downstream from the second inlet for separating the entering air stream into a multiplicity of air slices having planes parallel to the aforementioned side walls; said first and second separating mechanisms having cooperating components arranged to deliver individual ones of the first mentioned slices between individual ones of the first mentioned slices between individual ones of the second slices in sandwich relation; each air inlet located in a transverse wall adjacent a corner formed by the junction between its wall and the adjacent transverse wa'll; each air separating mechanism comprising spaced parallel air separator strips extending obliquely across respective ones of the aforementioned corners to intercept the respective air stream immediately after it passage through the respective inlet.

2. The system of claim 1 wherein each air separating mechanism takes the form of a frame structure made separate from the box, each frame structure comprising the aforementioned separator strips and mounting bars connected with said strips at their opposite ends; each frame structure being mounted within the box with its mounting bars extending along different ones of the box transverse walls.

3. The system of claim 2 wherein the transverse walls include four walls at right angles to one another whereby to define a rectangular box cross section; the air inlets being located adjacent two of the box corners remote from the air outlet wall, and the air separator strips extending obliquely across said remote corners to the approximate mid-point of the transverse wall which parallels the air outlet wall.

4. The system of claim 2 wherein the air separator strips for one of the inlets have their rear faces located to deflect air slices coming from the other inlet toward the outlet; said separator strips being spaced further apart than the width of individual strips.

5. The system of claim 4 wherein each separator strip is about one half as wide as the spacing between strips.

6. An air conditioning system comprising a mixing box having two parallel side walls, and first, second, third and fourth transverse walls extending therebetween; means defining a first air inlet in the first transverse wall; means defining a second air inlet in the second transverse wall; means defining an air outlet in the third transverse wall; first volume control means for the air flowing through the first inlet; second volume control means for the air flowing through the second inlet; first mechanism immediately downstream from the first inlet separating the entering air stream into a multiplicity of air slices having planes parallel to the aforementioned side walls; second mechanism immediately downstream from the second inlet for separating the entering air stream into a multiplicity of air slices having planes parallel to the aforementioned side walls; said first and second separating mechanisms having cooperating components arranged to deliver individual ones of the first mentioned slices between individual ones of the second slices in sandwich relation; each volume control means comprising butterfly dampers mounted for rotation about axes extending normal to the box side walls; each air inlet being formed as a rectangular air entrance opening, the dimension of each opening paralleling the aforementioned damper axes being materially greater than the dimension normal to said axes, whereby the air flows are controlled by relatively small numbers of elongated dampers.

References Cited UNITED STATES PATENTS 3,212,424 10/1965 Davis 98-38 3,180,245 4/1965 Erickson et a1. 98-38 ROBERT A. OLEARY, Primary Examiner.

W. E. WAYNER, Assistant Examiner. 

